The Pastern Joint

Learning Outcomes

By the end of this article, you should aim to be able to:

1. Identify the bones and principal anatomical structures that make up the equine pastern.

2. Describe the important soft tissue structures associated with the proximal and distal interphalangeal joints.

3. Explain how the pastern contributes to limb movement, shock absorption and efficient locomotion.

Definition

The pastern is the region of the horse's limb located between the fetlock and the hoof. It contains the proximal phalanx, commonly referred to as the long pastern bone, and the middle phalanx, or short pastern bone. These bones form two articulations: the proximal interphalangeal joint, commonly called the pastern joint, between the proximal and middle phalanges, and the distal interphalangeal joint, or coffin joint, between the middle and distal phalanges. Although relatively small compared with other regions of the limb, the pastern plays an important role in maintaining alignment between the limb and hoof and in controlling the movement and loading of the distal limb.

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Anatomy

The proximal phalanx is the largest bone within the pastern and extends distally from the fetlock joint. It is relatively broad proximally and becomes narrower towards its distal end. Its distal articulation is with the middle phalanx at the proximal interphalangeal joint. The middle phalanx is shorter and more compact, extending from the pastern joint towards the distal interphalangeal joint. Distally, it articulates with the distal phalanx and is also associated with the navicular bone.

The pastern therefore forms an important link within the skeletal chain extending from the fetlock to the hoof. The shape, orientation and alignment of these bones influence the hoof-pastern axis and the way forces are transmitted through the limb. From a farriery perspective, understanding this relationship is essential because changes in hoof conformation can alter the mechanical loading experienced by the joints and supporting tissues of the pastern.

Soft Tissue Structures of the Pastern Joint

The pastern joint is stabilised by a combination of joint capsule, collateral ligaments and supporting structures. The collateral ligaments are positioned on the medial and lateral aspects of the joint and resist excessive sideways movement. A strong fibrous joint capsule surrounds the articulation and contains synovial fluid, which lubricates the joint and assists with nutrition of the articular cartilage.

The distal limbs of the superficial and deep digital flexor tendons pass along the palmar aspect of the pastern. The superficial digital flexor tendon continues distally and inserts on the proximal aspect of the middle phalanx, while the deep digital flexor tendon continues towards its insertion on the distal phalanx. The digital flexor tendon sheath facilitates smooth movement of these tendons as they pass through the region. The straight and oblique sesamoidean ligaments associated with the fetlock contribute to the overall suspensory and flexor support of the distal limb, while the distal sesamoidean ligaments provide additional support towards the pastern and coffin joints.

Function

The primary function of the pastern is to provide controlled movement between the fetlock and hoof while transmitting forces between the limb and ground. During weight bearing, the pastern undergoes controlled extension as the limb absorbs and redistributes loading. This movement is influenced by the bones, joint surfaces, ligaments and flexor tendons.

The pastern therefore contributes to shock absorption and efficient locomotion while maintaining stability of the distal limb. Its ability to flex and extend also allows the hoof to remain appropriately positioned as the horse moves over different surfaces. For the farrier, appreciating the interaction between pastern conformation, hoof balance and soft tissue loading is particularly important. Excessive or abnormal loading can contribute to joint and soft tissue problems, while appropriate hoof management can help maintain functional alignment and efficient force distribution through the limb.

Learning Questions

1. Which bones form the pastern and what joints do they create?

2. What is the difference between the proximal and distal interphalangeal joints?

3. Which soft tissue structures provide stability to the pastern joint?

4. How do the digital flexor tendons contribute to movement and support within the pastern?

5. Why is the relationship between hoof balance, the hoof-pastern axis and pastern function important to the farrier?